The present invention is related to a preparation method of 2,2,3,4,4,4-hexafluoro-1-butanol, and in particular to a low temperature and high pressure method for the preparation of 2,2,3,4,4,4-hexafluoro-1-butanol.
Japanese patent publication Nos. 200252823 (2002), 200253506 (2002), and 200253507 (2002) describe that a short-chain fluoroalkanol having the following formula (I) can be used as a solvent for an optical information recording dye of CD-R and DVD-R:
H(CFR1CF2)nCH2OHxe2x80x83xe2x80x83(I)
wherein the formula (I) represents 2,2,3,3-tetrafluoro-1-propanol, when R1=F, n=1; 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, when R1=F, n=2; and 2,2,3,4,4,4-hexafluoro-1-butanol (hereinafter abbreviated as HFB), when R1=CF3, n=1.
The methods for the preparation of HFB published in the literature include reacting hexafluoropropene and methanol under irradiation of light, heating and in the presence of a free radical initiator, wherein
J. Fluorine Chem., 291,28 (1985) and apatent application with a publication number of CS268247 disclose a synthesis method by using irradiation of light. This method requires special lighting equipment, and suffers an abrupt change in temperature or pressure during the reaction. Therefore, this method is not easy to be put into mass production.
U.S. Pat. No. 3,927,129 (1975) discloses a high-temperature synthesis method, wherein hexafluoropropene and methanol are reacted at 280xc2x0 C. for four days, and the yield is 85%. The yield drops to 31%, when the reaction temperature is 240xc2x0 C. The high temperature and long reaction time are adverse factors for a mass production based on this synthesis method.
PCT application WO 01/02329 (2001) discloses a process for producing fluoroalkanol including heating methanol in an autoclave at a temperature of 125xc2x0 C., separately and continuously adding hexafluoropropene and a free radical initiator of di-t-butyl peroxide in methanol to the autoclave. A high-pressure feeding apparatus is required for the additions of hexafluoropropene and the free radical initiator. Moreover, the rates of the additions must be controlled accurately to avoid dangers caused by an abrupt increase in temperature or pressure in the autoclave. For an one-liter autoclave only 125 g of hexafluoropropene was reacted per batch.
PCT application WO 01/62694 (2001) discloses a process for preparation of HFB including heating methanol, a free radical initiator and a small amount of hexafluoropropene in an autoclave, and feeding hexafluoropropene during the reaction. This process also requires high-pressure feeding apparatus, and suffers a continuous increase in reaction temperature. In Example 1 of this PCT application, the reaction temperature was increased from the starting 48xc2x0 C. to 75xc2x0 C. after 7-hour of hexafluoropropene feeding, wherein t-butylperoxy-2-ethyl hexanoate was used as a free radical initiator and an 1-L autoclave was used. A similar trend of reaction temperature increase was also observed in the other examples. Therefore, the rates of the hexafluoropropene feeding must be controlled accurately to avoid dangers caused by an abrupt increase in temperature or pressure in the autoclave. For the one-liter autoclave used in Example 1 of this prior art 277 g of hexafluoropropene was reacted per batch, and 5510 g of hexafluoropropene was reacted per batch for a 20-L autoclave used in Example 2. The product yield after distillation was about 75%.
The present invention provides a method for preparing 2,2,3,4,4,4-hexafluoro-1-butanol comprising reacting methanol and hexafluoropropene in the presence of a free radical initiator such as di-isopropyl peroxydicarbonate at 25-50xc2x0 C., preferably 40-50xc2x0 C., and a pressure of 100-300 psi in an autoclave for a period of time. An inert gas such as nitrogen and argon is added to the autoclave when the pressure is lower than 100 psi in the course of the reaction.
In the method of the present invention, preferably nitrogen is introduced to the autoclave so that the pressure is maintained at 200-300 psi.
In the method of the present invention, preferably methanol and hexafluoropropene is reacted with a molar ratio of hexafluoropropene to methanol of 0.2-1 at the beginning of the reaction, and no hexafluoropropene being added in the course of the reaction. More preferably, molar ratio of hexafluoropropene to methanol is of 0.3-0.4.
Preferably, said period of time for said reaction is 20-40 hours.
The present invention discloses a novel method for preparing 2,2,3,4,4,4-hexafluoro-1-butanol (HFB) by reacting methanol and hexafluoropropene in the presence of a free radical initiator at 25-50xc2x0 C. in an autoclave, wherein an insert gas including (but not limited to) nitrogen and argon may be added to the autoclave to maintain a pressure in the autoclave not lower than a predetermined value. The advantages of the present invention include: no addition of reactants during the reaction, no abrupt change in temperature, and increase in the amount of reactants reacted per volume of the autoclave per batch.
An example of the free radical initiator used in the method of the present invention is di-isopropyl peroxydicarbonate. The amount of the free radical initiator used ranges from 0.001 to 10, and preferably from 0.01 to 0.06, times of the weight of methanol used.